This invention relates generally to pulsed radar systems. Specifically, the present invention relates to alleviating the transmitter leakage into the receiver in a manner to optimize the radar sensitivity to targets at close ranges.
Radars are sometimes required to detect targets at very close ranges. A major source of interference in the close range detection process is the self-generated interference from the signal sent by radar transmitter. Because the isolation between the transmitter and receiver is finite, a portion of the instantaneous transmitted signal tends to enter or leak into the receiver.
In a non-coherent pulse radar, this "leakage" signal is rejected by receiver switch circuitry that keeps the receiver input signal path switched off during some portion of the transmitted signal but which hopefully switches this path on in time for the receiver to receive the reflected signal from the target. The time between the transmitted signal and the reflected signal decreases as the target and the radar come closer together. Accordingly, as the radar and the target come closer together a distance will be reached between them where the leading edge of the reflected signal will overlap the trailing edge of the leakage signal. Under these conditions, the receiver switch must attenuate the leakage signal enough to prevent its false detection as a target but this action also tends to attenuate close range reflected target signals since these overlap part of the leakage signal. Timing of the receiver switch turn-on therefore is critical for stable, maximum sensitivity to targets at close range.
Prior art radar systems, which will be described in more detail in a subsequent part of this specification, generally enable the receiver input path to become conductive at a fixed, predetermined time after the transmitted pulse is sent. This fixed turn-on delay is chosen for worst case conditions to assure that the leakage signal will not be mistaken as a target. Such designs based on worst case parameters unfortunately result in the radar sensitivity to close range targets being lower than it could potentially otherwise be when the actual parameters are not worst case.